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Re: Tall stud wall framing / IRC rant

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Jordan,

This helps me understand better.

Now that you point out that it is Fb', then I agree that there are
potentially issues with this table (in general I withhold final
judgment until I can review things myself).  Requiring someone to figure
out the modification factors from the NDS kind of defeats the purpose of
the NDS, in my opinion.  To some degree, even if it was just Fb (i.e. the
base bending stress value) there still might be some issues if the IRC did
not list Fb values for various species, since to me the intent of the IRC
(i.e. prescriptive design) is that one should not have to grab
"engineered design" documents like the NDS.

Now, I would argue that if the table footnote limits to snow load of 25
psf, then the contractor maybe ain't so bright or is just playing dumb to
try to get way with "doing the way I have been doing it".  That limitation
seems pretty obvious to me.  As does the 6' trib width (assuming that the
the person reading it understands what a trib width is), although
admittedly a 6' trib width is rather restrictive (but it is possible to
have a 10' wide room...I have seen plenty of houses with bedrooms that
have one dimension that is 10'...so it is entirely possible to have an
intertior bearing wall 10' away from an exterior wall).

As to the misleading bit...sure, it is possible that it is misleading.
But, then I will say it again...anything can be misleading if you don't
read the whole thing.  You say that "I don't want folks whining that they
have to come to me because they need me to tell them that a 2x6 wall is
okay for a 12' gable end."  I would say then that you are in the wrong
profession, 'cause it should be pretty obvious that you will ALWAYS
encouter people who will whine about having to hire an engineer (and/or
architect) to design all or part of their house.  We could get rid of ALL
the misleading stuff in IRC, yet you would still be face with situations
where an architect and/or engineer must be involved and the home
owner/client/builder will complain about it.

And when it really comes down to it, it really sounds like to me that the
problem you are facing is just another contractor is doing the good ol' "I
been doing it this way for XX number of years without any problems" song
and dance.  That is where I am now temped to respond with "I have been an
asshole for XX number of years, so just do it the way that I told you to
do it."  <grin>

As to your mortgage example...misleading, yes.  Doesn't matter to me.  If
it is there to be read and is not deliberately "hidden" (i.e. in fine
print SO small that you cannot really read it), but you chose not to read
the fine print and get burned by it...tough luck...you should have read it
all.  Do such misleading things potentially waste my time by bringing me
in the door on what seems like a good deal only to find out
otherwise...yep.  But, then if I find that to be the case, I walk away and
more than likely that company won't ever get business from me in the
future.

In the end, to me it is part of our headline society.  We like things in
easy little snippets that don't require much work or effort on our part.
For many, when we have to spend a little more time or effort, then it is
not long worth it and we get annoyed.  And as a result, advertisers,
companies, the government, and all types of others just feed that desire.
They give you a little bit of the truth and now where near the whole
truth.  And most of the time blithely accept it and wander on to the next
thing in ignorant bliss.  At least until the $hit hits the fan.

OK, enough "soapboxing" for me.

Regards,

Scott
Adrian, MI


On Sat, 27 Aug 2005, Jordan Truesdell, PE wrote:

> Oh, I don't disagree that the table is accurate. I believe that it is
> misleading. Its no different that advertising a mortgage rate of 2%, and
> putting an early payoff penalty, 5 discount points, and a 25% LTV ratio
> in the fine print.  I don't want the table removed - I don't want folks
> whining that they have to come to me because they need me to tell them
> that a 2x6 wall is okay for a 12' gable end.
>
> It is my opinion that the table is unclear.  The limitations on material
> used are given in terms of Fb' and E, and Fb' requires the application of
> up to two adjustment factors (Cf and Cr) to the base Fb.  Values of Fb
> and E, as far as I know, are not provided in the IRC or at the point of
> sale, so there's no way for a contractor to verify whether the table
> applies. I would argue that most building inspectors would not be able to
> find the values and properly apply the adjustments, even if they happened
> to have a copy of the NDS in their truck when the go to the job site.
> Allowing only 6' of tributary load from a floor or roof is practically a
> non-loadbearing condition; why not just say "non-loadbearing" in the
> title? How many roof spans have you seen in the past year that are less
> than 10' (1/2span+1' overhang)?
>
> My point is that the IRC should give tables and values that are
> appropriate for residential construction. To argue that the 5th
> percentile residential contractor will be able to sort out *and
> calculate* engineering data to determine the appropriate grades and
> species, and for the 5th percentile building official to be able to
> verify this information in the 30 minutes they have to inspect 4000SF of
> residential framing is asking way too much. This table is misleading at
> best, and dangerous at worst.
>
> There's no question that the builder, in this case, has it wrong. But
> after failing the inspection, he went back to the code and - even after
> reading it "carefully" - he still got it wrong.  And this is a builder
> with two full time, in-house designers with architectural experience
> building custom homes in the top 10-15% of the local market.  The
> designer was quite indignant about the failed inspection, too. Its his
> argument that they've built many walls very similar to this (it's from
> one of their popular "base" plans which they customize) and have never
> had a problem.  The builder has only been around for about 10-12 years,
> and we have not had anywhere near a code wind, snow, or seismic event in
> that time (15y, 40y, and 130y respectively, I believe). They really don't
> understand that the load criteria is 50 years. They can't be sued after
> 10 years (statue of repose in VA, if I remember correctly), and if they
> didn't have to design beyond that point they wouldn't.
>
> BTW did you know that if you use the tables in the IRC to design your
> rafters, and you put a collar tie at the upper third of the rafter, all
> of the spans in the IRC tables must be multiplied by a factor of 0.5? Its
> right there in the code, but I have yet to find a framer who has known
> that. These guys (and gals) are not math or code wizards. Lets not
> pretend that they are.
>
>
>
> Scott Maxwell wrote:
>
>  Jordan,
>
> I am confused.
>
> Why exactly are you ranting at the IRC/IRC folks?
>
> Is there anything technically wrong with what is in the table (when
> accounting for the limitations/footnotes) when compared with an
> "engineered design"?  In other words, if you calc stuff out for
> situation that meets the limitations that you listed (i.e. snow load of
> 25 psf or less, trib width of less than 6 ft, Fb less than 1310 psi [is
> that supposed to be Fb, Fb' or Fb*?], etc), would 2x6s work for a 18
> foot tall wall?
>
> Is the table unclear?  And by this I mean that if someone reads ALL the
> information in the table it reasonable to understand that they might come
> to a different conclusion than someone else.  I don't consider something
> unclear just because the limitations are not listed in big (24 point),
> bold letter but rather in footnotes that might be small.
>
> I guess that if I am understanding correctly, you issue is not that the
> information in the table is wrong (at least that is not what you seem to
> say), but rather than because is has such a limited practical use, it
> should not be in the code cause in this situation it made your life
> difficult because someone did not read all of it.  So because of that, you
> want it gone from the code.
>
> Let's look at if from the other side.  Let's say we get ride of it from
> the code.  Now, say there is a project somewhere that is being designed
> per the IRC (i.e. prescriptively) that DOES fit that criteria.  In this
> situation, 2x6s would now NOT be permitted (this all assumes that the
> information is technically accurate).  So, on this project the client
> would have to pay for 2x8s when technically 2x6s would work.  Now, we have
> just reinforced that good old mantra that contractors love to change:
> "Boy, is this way over engineered" (whether true or not).
>
> I guess in the end I am wondering if you want the IRC (and other model
> codes) to put a big note in the front of the code in big, bold letters
> that reads: "Idiots, this includes people who are otherwise smart that
> just don't read all the requirements, shall not use this documents".  To
> be frank, this would also put a lot of engineers out of business as there
> are lot of people, engineers included, who don't always read all the
> "instructions".
>
> So, I think you should be ranting at the foreman and designer.  After all,
> the foreman appear to have been WRONG.  The IRC apparently does _NOT_
> permit the use of 2x6s in your particular case (you mentioned 30 psf snow
> load as well as trib width of 17 feet, I believe)...altough s/he is
> correct that there are situations (albit very limited) when the IRC does
> permit it.
>
> Now, if I am wrong in that you believe the information in the table (even
> when factoring in the limitations) is inaccurate when compared with
> a comparable engineered design, then maybe the code needs to be changed.
>
> Regards,
>
> Scott
> Adrian, MI
>
>
> On Sat, 27 Aug 2005, Jordan Truesdell, PE wrote:
>
>
>
>  I had a meeting today in which  a residential foreman  argued that an
> 18' tall stud wall needed only be 2x6 studs on 16" centers according to
> the table in the IRC. Well, I'd had this discussion with the designer a
> week previous, where I showed him the output of an analysis that
> indicated a 2x8 was necessary for this framing. The designer also
> thought that 2x6 was okay, but didn't reference the IRC.
>
> I looked it up tonight, just to see if the IRC was sharpening their
> pencils a little much again, and found that the table, R602.3.1 to be
> exact, does indeed show 2x6s for an 18' stud wall.  Curious, I read the
> notes at the bottom and found the caveats listed to be almost
> ridiculously restrictive, such that the designs are practically unusable
> in a good bit of the country. Snow load must be less than 25psf - I
> assume this is ground snow load, since there is no formula in the IRC to
> convert to a roof snow load (locally we're 30).  Fb must be > 1310psi.
> Well, even with a repetitive and size factor added, No.1 SPF - the most
> common stud material around me (and on the east cost, I suspect) comes
> out to 1308psi. Add in an E of 1.6x10^6, and the list of lumber species
> and grades gets mighty short - #2 S. Pine and Doug.Fir are the only
> framing species that fit the criteria.  Here in the east there are no DF
> studs, and S.Pine smaller than 2x8 is found only in treated lumber and
> trusses without a special order.  Tributary width for vertical loads
> must be less than 6'.  Unless you've got lots of interior bearing, or
> are only checking gable end walls, that makes for pretty small rooms and
> no trussed roofs. And if it weren't obvious from the material
> properties, Stud grade studs are not permitted (nor are utility,
> construction, or No 3).
>
> It just makes me shake my head.  Even if this particular job didn't have
> a 17' horizontal span without a sole-to-top plate stud, and if they
> hadn't framed a two story wall by stacking two 9' tall walls, and if
> they hadn't used 2x4s, and even if it wasn't backing up brick veneer,
> there are still 5 different criteria that disallow the use of this
> chart.  And yet, the chart says 2x6 on 16" centers works, so they figure
> it's correct, and I'm full of *expletive* for telling them they should
> have used at least 2x8s. Worst, with their openings they'll need 3/4T of
> steel to fix the problem without packing the wall to thicker than
> 3.5".   It think the #2 S. Pine and Doug.Fir needs to be in the title,
> and they may as well just say "non-bearing-walls only", with a little
> note at the bottom for an exception for walls with tributary widths less
> than 6' and snow loads of 25psf or less.
>
> I know that moaning and complaining here won't get the code changed (and
> I'm honestly not sure whose ear to chew on to try and get it changed),
> but are the rest of you doing small jobs like this running into similar
> problems? If so, how do we fix the code language so that mistakes are
> less likely?  Even the best inspectors can't remember all the notes and
> subnotes across all of the disciplines in a couple thousand pages of code.
>
> Jordan
>
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